FIGS. 4(a) to 4(d) show a principle of patterning a mask pattern, which is generally used, in which FIG. 4(a) shows cross-sectional structures of a mask pattern and exposed wafer, FIG. 4(b) shows the amplitude distribution of the incident light on the mask pattern, FIG. 4(c) shows the amplitude distribution of light on a wafer transmitted through the mask pattern, and FIG. 4(d) shows the intensity distribution of the light on the exposed wafer.
In these figures, reference numeral 30 designates a mask pattern comprising light shielding films 1a, 1b, and 1c and a glass substrate 3. The light shielding films 1a, 1b, and 1c comprise metal such as Cr disposed on a first surface of the glass substrate 3. Reference numeral 4 designates monochromatic light incident on a second surface of the glass substrate 3. Reference numeral 40 designates a wafer which is to be exposed with the light 4 transmitted through the mask pattern 30 comprising a substrate 41 and a resist layer 42 disposed on the substrate 41.
In FIG. 4(a), when exposure light 4 having a single wavelength is incident on the mask pattern from above, the amplitude distribution of the incident light on the mask pattern 30 has the same phase as shown in FIG. 4(b). The amplitude of the incident light which has passed through the mask pattern 30 is distributed on the wafer 40 as shown in FIG. 4(c). In FIG. 4(c), the broken line represents the amplitude distribution of the light on the mask pattern 30 and the solid line represents the amplitude distribution of light on the wafer 40. When the light incident on the mask pattern 30 has the same phases and the light shielding film 1b provided in the aperture between the shielding films 1a and 1c is a fine pattern, diffracted diffraction occurs, thereby resulting in the amplitude distribution as shown by the solid line. Hence, the intensity distribution of the incident light on the wafer 40 is as shown in FIG. 4(d) and fine resist patterns cannot be produced on the substrate 41.
A phase-shifting method that has been developed in order to solve the above-described problems will be explained.
FIGS. 5(a) to 5(d) show a principle of patterning by using the phase-shifting method, in which FIG. 5(a) shows a cross-sectional view of a mask pattern in the phase-shifting method, FIG. 5(b) shows the amplitude distribution of the incident light on the mask pattern, FIG. 5(c) shows the amplitude distribution of light on the wafer which is to be exposed with the light transmitted through the mask pattern, and FIG. 5(d) shows the intensity distribution of light on the wafer transmitted through the mask pattern.
In these figures, reference numerals 1a, 1b, and 1c designate light shielding films, reference numeral 3 designates a glass substrate, reference numeral 2 designates a transparent thin film comprising an insulating film such as SiO or SiN for shifting the phase of exposure light (hereinafter referred to as a shifting film), and reference numeral 30 designates a mask pattern comprising the light shielding films 1a, 1b, and 1c, the glass substrate 3, and the shifting films 2. Reference numeral 4 designates monochromatic light. Reference numeral 40 designates a wafer which is to be exposed with the light 4 transmitted through the mask pattern 30 comprising a substrate 41 and a resist layer 42 disposed on the substrate 41.
In FIG. 5(a), the shifting film 2 is produced to invert the phase of the light transmitted through shifting film 2 by 180 degrees and the thickness thereof is represented by: EQU d=.lambda./2 (n-1)
where, d is thickness of the shifting film, ,.lambda. is wavelength of the light, and n is refractive index of the shifting film.
When the monochromatic light 4 is incident from above on the mask pattern 30 on which the shifting film 2 is produced to a required thickness d, the light at a places in the pattern where light shielding film is absent and where the shifting film 2 is present has a difference of 180 degrees in phase relative to the light at a place in the pattern where light shielding film is absent and the shifting film 2 is also absent. Therefore the amplitude distribution of light as shown in FIG. 5(b) appears on the mask pattern 30. The light which has passed through the mask pattern 30 reaches the wafer 40, and the light on the wafer 40 has the amplitude distribution of FIG. 5(c). In FIG. 5(c), the dotted line represents the amplitude distribution of the light on the mask pattern 30, and a solid line represents amplitude distribution of light on the wafer 40. As shown in this figure, since the amplitude of light on the mask pattern 30 varies due to inversion of the phase at opposite sides of the light shielding film pattern 1b, there is a place at the light shielding film pattern 1b where the amplitude of light is zero regardless of light diffracted where light shielding film is absent. In this way, as shown in FIG. 5(d), there is a place where the light intensity is zero where the light shielding film pattern 1b is located, on the substrate exposed with light, thereby enabling fine patterns to be produced.
The above-described phase-shifting method is effective in a repeating pattern of such as line and space.
On the other hand, in a case of a single pattern such as a space, a supplementary pattern which has an inverted phase is provided around the pattern to obtain fin patterns.
FIGS. 6(a) to 6(d) show a method of miniaturizing a single pattern using the phase-shifting method, disclosed in Japanese Patent Published Application No. 62-67514, in which FIG. 6(a) is a cross-sectional view of mask pattern, FIG. 6(b) shows an amplitude distribution of the incident light on the mask pattern, FIG. 6(c) shows the amplitude distribution of light on a wafer exposed with the light transmitted through the mask pattern, and FIG. 6(d) shows the intensity distribution of light on the wafer.
In all figures, like elements are given the same numerals, and reference numerals 1d to 1i designate light shielding films. Reference numerals 2c and 2d designate 180 degree phase-shifting films. Reference numeral 10 designates an aperture. Reference numerals 14a to 14d designate supplementary aperture patterns produced at both sides of the aperture pattern 10, the width of each of which is too narrow to be imaged by an optical exposure apparatus.
When patterns are transferred onto the resist film 42 provided on the substrate 41 using a mask pattern 30 shown in FIG. 6(a), the amplitude distribution of light on the mask pattern 30 is as shown in FIG. 6(b), the phase of light which has passed through the aperture patterns 14b and 14c is inverted with respect to that of light which has transmitted through the aperture patterns 14a and 14d. The amplitude and intensity distribution of light on the wafer 40 exposed with light are as shown in figures 6(c) and 6(d), respectively, and it is found that only the light which has passed through the aperture pattern 10 is largely transferred.
A method of producing the mask pattern of FIG. 5(a) will be described with reference to FIGS. 7(a) to 7(f).
Firstly, a light shielding film 1 comprising metal such as Cr is produced on the entire surface of glass substrate 3 by deposition or sputtering, and a resist film 11 is plated on the entire surface thereof. Next, the resist 11 is exposed with light to produce desired patterns using an electron beam exposure method. At this time, the light shielding film 1 is grounded to prevent the glass plate 3 from being charged with electric charges due to the light exposure (FIG. 7(a)).
Thereafter, resist patterns 11a to 11c are produced by development (FIG. 7(b)), and the light shielding film 1 is etched using the resist patterns 11a to 11c as a mask to produce light shielding film patterns 1a to 1c, and then the resist patterns 11a to 11c are removed (FIG. 7(c)).
Thereafter, the entire surface of the partially completed device is plated with resist 12 for producing a shifting film and exposed with an electron beam by an electron beam exposure method (FIG. 7(d)), and thereafter it is developed to produce a resist pattern 12a and 12b. Thereafter, a shifting film 2 comprising a transparent thin film such as SiO or SiN is vapor deposited to a desired thickness (d) using the resist pattern 12a and 12b as a mask (FIG. 7(e)), and then a shifting film pattern 2 is produced by lift-off (FIG. 7(f)).
Here, in the process of electron beam exposure of the resist film of FIG. 7(d), light shielding film pattern 1c is required to be grounded or a metal film is required to be formed on the light shielding film pattern 1c to prevent the substrate 3 from being charged by electric charges.
The mask pattern of FIG. 6(a) is produced by an electron beam exposure method in the same way as the above-described method.
The conventional phase-shifting methods used in the line-and-space repeating pattern and single pattern, both have problems in the method of producing the mask pattern 30.
In the prior art production method, photoresist 11 is plated on the glass substrate 3 which is covered with the light shielding film 1, the surface exposed using the electron beam exposure method and developed to produce resist pattern 11a to 11c light shielding film patterns 1a, 1b, and 1c are produced by etching using the resist pattern 11a to 11c as a mask, and further resist patterns 12a and 12b are produced by using electron beam exposure method and development, and shifting film 2 is produced using the lift-off method. When the electron beam exposure is carried out, grounding is required to prevent the substrate 3 from being charged by irradiation with the electron beam.
However, when the resist 12 is exposed, the light shielding film which is to be grounded is patterned, and light shielding film patterns 1a to 1c are discontinuous on the glass substrate. Therefore, only one pattern such as pattern 1c can be grounded, and the portion between the light shielding films 1a and 1b is not grounded, whereby electrons charge that portion of glass substrate 3.
This charging of substrate causes problems as in the following.
Firstly, in the process of FIG. 7(d), when the position of resist 12 to be exposed is mark-detected relative to the light shielding film patterns 1a and 1b, the mark-detected position is shifted due to the influence of electric charge collected at surface of glass substrate 3 at the time of electric beam scanning, which causes a deviation in the position of the shifting film.
Secondly, as shown in FIGS. 8(a) and 8(b), in a case where only a pattern 1d among light shielding film patterns 1a to 1d is grounded at the time of exposure, the surface of glass substrate 3 is not charged in the vicinity below the light shielding film 1d but is charged at the other portions of the surface of glass plate such as those between the light shielding films 1a and 1b and under the light shielding film 1c (FIG. 8(a)). When a shifting film is deposited by evaporation in this state, the shifting film 2' produced between the shielding films 1c and 1d becomes positionally deviated to the side of the light shielding film 1d, influenced by electric charges stored at a between the shielding films 1a and 1b as shown in FIG. 8(b).
That is, in the prior art mask pattern production method using the phase-shifting method, the substrate is likely to be charged by using the electron beam exposure method, and it is impossible to obtain a desired shifting film pattern just on the light shielding film with high precision. Therefore, there is a large obstacle when the mask pattern is desired to be fine.